Fixed #9602 -- Added AdminSite.get_model_admin().

This allows retrieving an admin class for the given model class without
using internal attributes.

6 files changed, 66 insertions, 35 deletions

diff --git a/django/contrib/admin/checks.py b/django/contrib/admin/checks.py
index 45d895dff0..f5aa9b55d4 100644
--- a/django/contrib/admin/checks.py
+++ b/django/contrib/admin/checks.py
@@ -220,6 +220,8 @@ class BaseModelAdminChecks:
         ManyToManyField and that the item has a related ModelAdmin with
         search_fields defined.
         """
+        from django.contrib.admin.sites import NotRegistered
+
         try:
             field = obj.model._meta.get_field(field_name)
         except FieldDoesNotExist:
@@ -234,8 +236,9 @@ class BaseModelAdminChecks:
                     obj=obj,
                     id="admin.E038",
                 )
-            related_admin = obj.admin_site._registry.get(field.remote_field.model)
-            if related_admin is None:
+            try:
+                related_admin = obj.admin_site.get_model_admin(field.remote_field.model)
+            except NotRegistered:
                 return [
                     checks.Error(
                         'An admin for model "%s" has to be registered '
@@ -248,19 +251,20 @@ class BaseModelAdminChecks:
                         id="admin.E039",
                     )
                 ]
-            elif not related_admin.search_fields:
-                return [
-                    checks.Error(
-                        '%s must define "search_fields", because it\'s '
-                        "referenced by %s.autocomplete_fields."
-                        % (
-                            related_admin.__class__.__name__,
-                            type(obj).__name__,
-                        ),
-                        obj=obj.__class__,
-                        id="admin.E040",
-                    )
-                ]
+            else:
+                if not related_admin.search_fields:
+                    return [
+                        checks.Error(
+                            '%s must define "search_fields", because it\'s '
+                            "referenced by %s.autocomplete_fields."
+                            % (
+                                related_admin.__class__.__name__,
+                                type(obj).__name__,
+                            ),
+                            obj=obj.__class__,
+                            id="admin.E040",
+                        )
+                    ]
             return []
 
     def _check_raw_id_fields(self, obj):
diff --git a/django/contrib/admin/filters.py b/django/contrib/admin/filters.py
index f6f6d0dd6f..197d39bf21 100644
--- a/django/contrib/admin/filters.py
+++ b/django/contrib/admin/filters.py
@@ -257,10 +257,16 @@ class RelatedFieldListFilter(FieldListFilter):
         """
         Return the model admin's ordering for related field, if provided.
         """
-        related_admin = model_admin.admin_site._registry.get(field.remote_field.model)
-        if related_admin is not None:
+        from django.contrib.admin.sites import NotRegistered
+
+        try:
+            related_admin = model_admin.admin_site.get_model_admin(
+                field.remote_field.model
+            )
+        except NotRegistered:
+            return ()
+        else:
             return related_admin.get_ordering(request)
-        return ()
 
     def field_choices(self, field, request, model_admin):
         ordering = self.field_admin_ordering(field, request, model_admin)
diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index b0635669e9..f9760664dd 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -160,6 +160,8 @@ class BaseModelAdmin(metaclass=forms.MediaDefiningClass):
 
         If kwargs are given, they're passed to the form Field's constructor.
         """
+        from django.contrib.admin.sites import NotRegistered
+
         # If the field specifies choices, we don't need to look for special
         # admin widgets - we just need to use a select widget of some kind.
         if db_field.choices:
@@ -185,23 +187,27 @@ class BaseModelAdmin(metaclass=forms.MediaDefiningClass):
             # rendered output. formfield can be None if it came from a
             # OneToOneField with parent_link=True or a M2M intermediary.
             if formfield and db_field.name not in self.raw_id_fields:
-                related_modeladmin = self.admin_site._registry.get(
-                    db_field.remote_field.model
-                )
-                wrapper_kwargs = {}
-                if related_modeladmin:
-                    wrapper_kwargs.update(
-                        can_add_related=related_modeladmin.has_add_permission(request),
-                        can_change_related=related_modeladmin.has_change_permission(
+                try:
+                    related_modeladmin = self.admin_site.get_model_admin(
+                        db_field.remote_field.model
+                    )
+                except NotRegistered:
+                    wrapper_kwargs = {}
+                else:
+                    wrapper_kwargs = {
+                        "can_add_related": related_modeladmin.has_add_permission(
                             request
                         ),
-                        can_delete_related=related_modeladmin.has_delete_permission(
+                        "can_change_related": related_modeladmin.has_change_permission(
                             request
                         ),
-                        can_view_related=related_modeladmin.has_view_permission(
+                        "can_delete_related": related_modeladmin.has_delete_permission(
                             request
                         ),
-                    )
+                        "can_view_related": related_modeladmin.has_view_permission(
+                            request
+                        ),
+                    }
                 formfield.widget = widgets.RelatedFieldWidgetWrapper(
                     formfield.widget,
                     db_field.remote_field,
@@ -246,8 +252,13 @@ class BaseModelAdmin(metaclass=forms.MediaDefiningClass):
         ordering.  Otherwise don't specify the queryset, let the field decide
         (return None in that case).
         """
-        related_admin = self.admin_site._registry.get(db_field.remote_field.model)
-        if related_admin is not None:
+        from django.contrib.admin.sites import NotRegistered
+
+        try:
+            related_admin = self.admin_site.get_model_admin(db_field.remote_field.model)
+        except NotRegistered:
+            return None
+        else:
             ordering = related_admin.get_ordering(request)
             if ordering is not None and ordering != ():
                 return db_field.remote_field.model._default_manager.using(db).order_by(
diff --git a/django/contrib/admin/sites.py b/django/contrib/admin/sites.py
index 1e289876f8..41ce85db79 100644
--- a/django/contrib/admin/sites.py
+++ b/django/contrib/admin/sites.py
@@ -121,7 +121,7 @@ class AdminSite:
                 )
 
             if self.is_registered(model):
-                registered_admin = str(self._registry[model])
+                registered_admin = str(self.get_model_admin(model))
                 msg = "The model %s is already registered " % model.__name__
                 if registered_admin.endswith(".ModelAdmin"):
                     # Most likely registered without a ModelAdmin subclass.
@@ -166,6 +166,12 @@ class AdminSite:
         """
         return model in self._registry
 
+    def get_model_admin(self, model):
+        try:
+            return self._registry[model]
+        except KeyError:
+            raise NotRegistered(f"The model {model.__name__} is not registered.")
+
     def add_action(self, action, name=None):
         """
         Register an action to be available globally.
diff --git a/django/contrib/admin/utils.py b/django/contrib/admin/utils.py
index bb5f950122..92ef1639b4 100644
--- a/django/contrib/admin/utils.py
+++ b/django/contrib/admin/utils.py
@@ -144,7 +144,9 @@ def get_deleted_objects(objs, request, admin_site):
         no_edit_link = "%s: %s" % (capfirst(opts.verbose_name), obj)
 
         if admin_site.is_registered(model):
-            if not admin_site._registry[model].has_delete_permission(request, obj):
+            if not admin_site.get_model_admin(model).has_delete_permission(
+                request, obj
+            ):
                 perms_needed.add(opts.verbose_name)
             try:
                 admin_url = reverse(
diff --git a/django/contrib/admin/views/autocomplete.py b/django/contrib/admin/views/autocomplete.py
index 130848b551..051b9a31b9 100644
--- a/django/contrib/admin/views/autocomplete.py
+++ b/django/contrib/admin/views/autocomplete.py
@@ -74,6 +74,8 @@ class AutocompleteJsonView(BaseListView):
         Raise Http404 if the target model admin is not configured properly with
         search_fields.
         """
+        from django.contrib.admin.sites import NotRegistered
+
         term = request.GET.get("term", "")
         try:
             app_label = request.GET["app_label"]
@@ -97,8 +99,8 @@ class AutocompleteJsonView(BaseListView):
         except AttributeError as e:
             raise PermissionDenied from e
         try:
-            model_admin = self.admin_site._registry[remote_model]
-        except KeyError as e:
+            model_admin = self.admin_site.get_model_admin(remote_model)
+        except NotRegistered as e:
             raise PermissionDenied from e
 
         # Validate suitability of objects.